GameMaker is a tool that allows the creation of video games using drag and drop action sequences or a sandboxed scripting language known as Game Maker Language.
YoYo Games has published in its blog, the first two parts of a series showing how to create a Commodore 64 emulator using its game creation tool.
If you are interested on learning a bit how to build an emulator, that a good way to go.
Link: YoYo Games Blog – Part 1 and Part 2
Source: Vintage is The New Old